15° 



DISCOVERY REPORTS 



Text-fig. 67 presents the affinities of the ascidian faunas as shown by the species in the ' Discovery ' 

 collection, and for comparison the sponge faunas of the same areas based on Burton's (1932) figures. 



Most of the species of ascidians found round the main part of the Antarctic continent also occur in 

 the Graham Land region, but progressively fewer in South Georgia, Kerguelen, the Falkland- 

 Patagonian region, and the Campbell-Auckland-Macquarie Islands region. 



Similarly, amongst the species of the Graham Land region, a high proportion is also known from 

 the rest of the Antarctic continent, and fewer from the remaining regions. 



Of the South Georgia species nearly half are also known from the Falkland-Patagonian region and 

 also from Kerguelen, and smaller proportions from elsewhere. 



Amongst the species from the Falkland-Patagonian region more than half also occur in South Georgia. 



The ascidian faunas therefore show the following affinities. In the high Antarctic the closest ties 

 are between the main part of the continent and the Graham Land region, which is no more than a 

 peninsula projecting into somewhat lower latitudes, but still well south of the Antarctic convergence. 

 The Antarctic continent including Graham Land, shows its closest affinity with South Georgia. 

 The latter region, however, has more species in common with the Subantarctic Falkland-Patagonian 

 region. So far as ascidians are concerned South Georgia occupies a position intermediate between the 

 true Antarctic and the true Subantarctic, a fact probably resulting from the colonization of South 

 Georgia from South America and the Falkland Islands via Burdwood Bank on the one hand and 

 from Graham Land via the South Orkney Islands on the other hand. South Georgia lies in the path 

 of material carried by the West Wind Drift from the southern end of South America and from the 

 northern end of the Graham peninsula. 



The affinities of the sponge faunas (Text-fig. 67) agree quite well with those shown by the ascidian 

 faunas. But the sponge faunas of South Georgia and the Falkland-Patagonian region have more in 

 common with those of the Antarctic continent (including Graham Land) than is the case in ascidians. 



